"WELDING MACHINE FOR POLYESTER FILMS

FIELD OF APPLICATION

The present invention relates to a welding machine for polyester films.

In particular, the present invention relates to an ultrasound welding machine for polyester films.

In particular, the present invention relates to an ultrasound welding machine for polyester films for the production of rubber articles, in particular in the automotive industry.

PRIOR ART

Thermoplastic materials, as the term itself says, are heat-sensitive plastic materials and can be transformed, moulded and welded by heating.

Ultrasound welding is a technological process that makes it possible to obtain the melting of thermoplastic materials by means of mechanical vibrations, expressed in microns, at a high frequency, ranging between 15 and 50 kHz. The friction developed by the high-frequency vibrations, generates heat and melting of the parts occurs without there being any direct thermal input (hot plate).

The main sectors requiring the use of this technique are the automotive industry, the technical products manufacturing sector, the medical sector and in general all sectors where objects are produced which have to be assembled and in which the mechanical characteristics and tightness must meet high standards.

Normally, ultrasound welding acts in a particular area of parts, which is called a "welding joint". It must be appropriately sized based on the specific application. In some cases, in particular in the welding of thermoplastic films, this possibility does not exist and it is the equipment which favours assembly.

In particular, for splicing thermoplastic films and synthetic fabrics, welding can be performed in different ways depending on the use, materials and technical characteristics that the splice must have.

The most used techniques are fundamentally three in number:

- Use of thermal welding machines

- Use of glues or adhesives

- Use of traditional sewing

In the first technique, the thermal welding machines have the characteristic of melting the parts to be joined by means of a thermal input determined by friction or by heat through direct contact. The parts are subjected to a push pressure during the welding process.

These are techniques without weld deposit and their operating principle is based on the thermoplastic characteristic of the materials to be spliced.

The materials are brought to the melting temperature and pressed against each other so that the interpenetration of the two favours a watertight weld.

In the second technique, the use of glues or adhesives or traditional sewing achieves a splice using added material.

In the case of the use of glues, specific glue is deposited between the two materials according to their technical characteristics.

With regard to the use of adhesives, the parts to be spliced are joined with adhesive tapes.

In the third technique, traditional sewing with a needle and thread is used.

The choice among these technologies is often conditioned by the type of materials to be joined, the mechanical characteristics of tightness of the joint, the speed and time necessary for performing the welding and the cost of the investment necessary for the machinery.

The known techniques, however, are largely inadequate and unsatisfactory because there are materials which cannot be thermally treated, as their characteristics would be modified if they were heated.

In other materials, use cannot be made of glues except with the use of special chemical agents and with very long reaction times.

Other materials cannot be sewn because they must have characteristics of watertightness after being joined. One aspect that is not of minor importance is undoubtedly the logistics and environmental conditions where this splicing must take place. The dimensions of the parts to be joined also often represent a problem that determines the impossibility of using machinery.

Another very important aspect is undoubtedly the verification of the technical characteristics that the splice must have immediately and during use of the manufactured article.

One highly specific sector involves the splicing of films made of polyester and is closely linked to the production of rubber articles, in particular in the automotive industry.

Polyester film, in various widths and lengths, must be spliced to increase the length of the film itself or for repairs due to mechanical-thermal stress during its use in production.

The most widely used known technique consists in the use of adhesive tapes.

Splicing film with adhesive tape is a simple and completely manual technique. Once the part to be spliced is identified, the operator must cut the damaged part.

Before the two parts are assembled using adhesive tape, the films must be aligned.

As can be inferred from the completely manual implementation of this technique, the time required for the splicing operation is long and the mechanical tightness of the splice is modest.

Particular care must be taken to ensure the linearity of the splice so that the film is always perfectly aligned.

There is thus a greatly felt need for an improved technique for splicing polyester films which overcomes the disadvantages still present today.

The object of the present invention is to realize a welding system that ensures a polyester film splice with high mechanical tightness.

A further object of the present invention is to realize a welding system that ensures a polyester film splicing in a short time. SUMMARY OF THE INVENTION

These and other objects are substantially achieved by a welding system for polyester films according to what is described in the appended claims 1 to 12.

The system, according to the invention, mainly achieves the following technical advantages/effects:

• the splicing of the polyester films takes place very rapidly;

• the mechanical tightness of the splice is particularly high;

• the splice can be realized on polyester films of different structure and size.

Additional features and advantages will be more apparent from the detailed description of a preferred, but non-exclusive embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

This description is provided here below with reference to the appended figures, likewise provided purely by way of example, in which:

- figure 1 a shows a schematic side view of the welding system of the invention;

- figure 1 b shows a schematic plan view of the welding system of the invention;

- figure 2 shows a detail of the system of the preceding figures;

- figure 3 shows another detail of the system of the preceding figures;

- figure 4 shows a detail of the weld of a polyester film according to the invention;

- figures 5a and 5b show schematic views of a polyester film subjected to cutting according to the invention;

- figure 6 shows a detail of an ultrasonic sonotrode according to the invention.

DETAILED DESCRIPTION

The invention describes a welding system that performs splicing of films made of polyester, in particular mylar, by means of ultrasound. By means of this new system, the splicing takes place very rapidly and the mechanical tightness of the weld is particularly high.

The system of the invention comprises a welding line comprising, in turn, a cutting assembly configured for cutting the polyester film, at least a repositioning assembly for repositioning the cut film, an ultrasound welding assembly configured for welding the cut film and a control unit configured for controlling the welding line.

With particular reference to figures 1 a and 1 b, the welding system comprises a welding line 2 in which the polyester film 1 moves in an advancing direction A-A'.

The welding system comprises a station 20 which supplies the polyester film 1 and is configured for supplying the film along the advancing direction (A- A').

The supply station 20 comprises rotating means 21 configured for supporting a coil 23 of polyester film 1 to be repaired.

The welding system further comprises an exit station 120 comprising rotating means 121 configured for supporting a coil 123 of repaired polyester film 1.

Preferably, the rotating means 21 and 121 comprise a spindle.

Preferably, the spindles are motorized.

The welding system according to the invention comprises, as already said, the welding line 2.

With particular reference to figure 2, the welding line 2 comprises, in turn, a cutting assembly 60 configured for cutting the polyester film 1 near damaged areas of the film itself.

With particular reference to figure 5a, the cutting assembly 60 cuts a portion of film 65 depending on the damaged area detected.

The cutting assembly 60 thus defines two separate portions 1 a, 1 b of the film 1.

Preferably, the cutting assembly 60 is placed transversally relative to the advancing direction A-A'.

With reference to figure 2, the cutting assembly preferably comprises a cutting recess 61 in which a cutting blade slides (not shown in the figure). The cutting assembly is normally controlled by an operator.

Alternatively, or in addition, the cutting assembly 60 comprises a carriage with which the blade is associated; under the action of the carriage moving transversally to the advancing direction A-A', the blade acts on the film 1 , cutting it.

In this embodiment, the cutting assembly 60 is associated with a special control unit 63.

The control unit 63 is configured for:

• timing the cutting operation based on the feeding of the polyester film 1 along the advancing direction A-A';

• determining the size of the portion of film 65 to be cut based on the damaged area of film detected.

• determining the movement of the carriage for the actual cutting operation.

The welding system according to the invention further comprises at least a repositioning assembly 31 ,32 suitable for positioning the two portions 1a, 1b in a predefined mutual position P following the cut for a corresponding welding.

In other words, in position P the repositioning assemblies overlap the two portions of the film 1 that had been separated by the cutting assembly 60. Preferably, the welding system according to the invention comprises two repositioning assemblies 31 , 32.

The repositioning assemblies 31 , 32 are configured to move along the forward moving direction A-A' of the film 1.

Preferably, the assemblies are driven by pneumatic cylinders.

According to the invention, the repositioning assemblies 31 , 32 are configured to move the two portions 1a and 1 b in a mutual position P so that they partially overlap.

The entity of the overlap according to the invention is defined based on the mechanical characteristics it is desired to give to the weld.

In particular, such characteristics are determined as a function of one or more among:

• film thickness;

• film type and composition;

For example, a film can have a canvas weave or can be made simply of polyester. In the former case, the film's resistance is greater and the overlap will be greater in order to enable a better welding of the two portions 1a, 1 b. In the latter case, a smaller overlap will probably ensure efficient welding in any case.

Preferably, the overlap of the two portions falls in an interval of between 3 and 15 mm.

A specific control unit controls the movement of the positioning assemblies by actuating the cylinders.

The system of the invention comprises means for detecting the positioning assemblies 31 , 32, configured for detecting the positioning of the means 31 , 32 on the welding line 2.

Preferably, the detecting means comprise sensors mounted on the cylinders which detect the movement of the cylinder and, therefore, of the repositioning assembly along the forward moving direction A-A' of the film 1. Optionally, the movement of the cylinders can be motorized and the entity of the movement determined by means of a linear encoder associated with the cylinders.

The welding system according to the invention comprises an ultrasound welding assembly 40 configured for welding, by ultrasound, the two portions

1a and 1 b in the predefined position P.

The welding assembly 40 is disposed above the film 1.

The welding assembly 40 is disposed transversally to the advancing direction A-A', supported in particular by a weight-bearing bar 140.

Advantageously, according to the invention, the welding assembly 40 comprises a plurality of ultrasound generators 41 ,42,43.

The generators comprise respective welding abutments 141 , 142, 143 (fig.

6) and two lateral pressors 241 , 242 (fig. 6) mounted so that the two portions

1a and 1 b to be welded do not move during the welding operation.

The welding abutments 141 , 142, 143 can have differently designed shapes.

The welding assembly 40 further comprises a plurality of sonotrodes 341 ,

342, 343 configured for determining a vibration in the overlapping zone of the two portions 1 a and 1 b.

According to the invention, the sonotrodes 341 ,342,343 are also aligned transversally to the advancing direction A-A'.

The sonotrodes 341 , 342, 343 are coupled with the ultrasound generators 41 , 42, 43, and disposed below the film to be welded.

According to the invention, the ultrasound welding by the ultrasound generators 41 ,42,43 takes place in the overlapping zone of the portions 1a, 1 b to be welded simultaneously with a vibration applied on the same zone by the sonotrodes 341 , 342, 343.

A sonotrode is a tool that vibrates and comes into contact with the part involved in the welding.

It is configured for welding with low mechanical displacement and high frequencies.

It is made with a particular geometry, in accordance with the vibration and resonance frequency conditions of the system.

The sonotrode can be made with a flat contact surface; alternatively, it can be made with a particular profile to determine a welding abutment against the film with particular characteristics depending on the type of material to be welded, the thickness, width etc.

According to the invention, the sonotrode is configured to discharge the vibration only on the points of abutment. Otherwise, welding of the film would not be achieved.

In other words, if an abutment with a particular shape is used, the ultrasound emitted by the ultrasound generators 41 ,42,43 enables the material to be melted quickly by directing the vibration onto well-defined points so as not to alter the characteristics of the film.

The welding abutment, constructed with a particular geometry, is very rigid and endowed with a system of lateral pressors so that the two parts to be welded cannot move while the ultrasound is being delivered.

The material subjected to vibration absorbs sufficient energy for melting and controlling the welding cycle and enables splices with excellent characteristics to be obtained.

The vibration time, vibration amplitude, vibration frequency and the pushing force exerted on the parts to be welded are the fundamental parameters for this type of technology and are defined experimentally.

With reference in particular to figure 3, according to the invention, the use of three sonotrodes working simultaneously coupled with the three ultrasound generators ensures the obtainment of an effective linear weld in a reduced amount of time.

According to the invention, the ultrasonic sonotrodes 41 ,42,43 are configured for mutually independent adjustment.

The welding system of the invention further comprises driving means 50 (fig. 1 b) associated with the welding line 2 and configured so as to be able to vary its position transversally to the advancing direction A-A'.

In other words, the driving means 50 are configured for preventing the polyester film 1 from sliding in a transversal direction relative to the advancing direction A-A'.

In yet other words, the driving means 50 are movably associated with the welding line 2 and configured for preventing the polyester film 1 from sliding in a transversal direction relative to the advancing direction A-A'.

The driving means comprise dividers 50 configured so as to determine a guide for the sliding of the polyester film 1.

The driving means 50 ensure that the film 1 does not rotate relative to the advancing direction A-A' due both to the effect of the simple sliding and the effect of cutting by the cutting means. The driving means 50 are adjusted in position based on the width of the film

1 to be repaired in such a way as also to ensure an adequate tolerance that enables the film to slide with negligible friction against the dividers.

The system further comprises a supporting structure 10 configured to support the entry 20 and exit 120 stations, the cutting assembly 60, the welding assembly 40, the positioning assemblies 31 , 32 etc.

The welding system according to the invention also comprises a fundamental part controlling the welding line 2.

According to the invention, in fact, the welding system comprises a control unit 70 (fig. 1a, 1 b).

In general it should be noted that in the present context and in the claims below, the control unit 70 will be presented as divided into distinct functional models (memory modules or operating modules) for the sole purpose of describing the functions of the unit in a clear and complete manner.

In reality, the unit can consist of a single electronic device, duly programmed to perform the functions described, and the different modules can correspond to hardware and/or routine software entities belonging to the programmed device.

Alternatively, or in addition, these functions can be performed by a plurality of electronic devices over which the aforesaid functional modules can be distributed.

The control unit 70 can moreover rely on one or more processors to carry out the instructions contained in the memory modules.

The aforesaid functional modules can also be distributed over different local or remote computers based on the architecture of the network they reside in. The control unit 70 comprises a detecting module 71.

The detecting module 71 is configured for detecting the current position of the positioning assemblies 31 , 32.

The detecting module 71 is associated with the detecting means already described.

The control unit 70 further comprises a first repositioning module 72. The first repositioning module 72 is configured for positioning the repositioning assemblies 31 , 32 in the predefined position P.

Preferably, the first repositioning module 72 is configured for acting on pneumatic cylinders according to a predefined mechanically set variation.

Alternatively, or in addition, this predefined variation is also set by a suitable operating module together with the movement of the cylinders.

The control unit 70 further comprises a command module 73.

The command module 73 is configured for activating the welding assembly

40 as a function of a completed repositioning of the repositioning assemblies

31 , 32 in the predefined position P.

The control unit 70, according to the invention, comprises a second positioning module 74 configured for positioning the driving means 50 as a function of predefined positioning parameters P1 , such as the width of the film 1.

The control unit 70 comprises a plurality of control modules 75,76,77 of the sonotrodes 341 , 342, 343.

These modules are configured for an independent control of the sonotrodes 341 ,342,343.

According to the invention, each control module 75,76,77 is configured for regulating each respective sonotrode 341 ,342,343 as a function of one or more among:

o welding time;

o cooling time;

o push pressure;

o vibration amplitude.

The control unit 70 also comprises a plurality of control modules 78 of the ultrasound generators 41 , 42, 43.

In particular, the module 78 is configured to time the operation of ultrasound emission based on the type of film to be treated and its composition.

According to what has been described, the welding system operates as follows: after starting the conveyance of the film in the supply station 20, an operator checks when it needs to be spliced and decides to stop the drive motors.

In succession, the cutting means 50 proceed to cut the damaged part.

The two repositioning assemblies 31 , 32 are activated and the two portions 1a, 1 b of film are positioned in the ultrasound welding station in such a way as to partially overlap in position P.

Transversal alignment is ensured by specific driving means 50 which can be adjusted to adapt the machine to the various categories of films of different widths.

Once the portions 1a, 1 b are positioned in position P, a plurality of ultrasound generators 41 , 42, 43 endowed with respective welding abutments 141 , 142, 143 are made to rest on the film by means of suitable pressors 241 , 242 in such a way as to secure the film to be welded in place and so that the abutments come into contact with the film.

Below the film, three sonotrodes 341 , 342, 343 determine a vibration of the overlapping part of the two portions 1 a, 1 b simultaneously with the emission of ultrasound by the ultrasound generators 41 , 42, 43, thus bringing about the welding.

At the end of the welding, the motors are restarted and the rewinding of the coil continues in the exit station 120 until the operator decides on a new stop for a subsequent operation.

Welding of films was performed using an ultrasound system with a power of 2000 Watts and frequency of 20 kHz. The welding was performed on a standard Sirius Electric press model USPM equipped with a vibrating assembly with sonotrode.

The set parameters, for a film width of 190 mm, were:

- Welding time = 1.5 sec

- Cooling time = 1.5 sec.

- Push pressure = 3.2 bar

- Vibration amplitude = 76 micron p/p

These values are associated with the USPM press and can vary according to film thickness and type.

The invention presents multiple advantages:

using ultrasound technology it is possible to obtain a very resistant splice and the welding time is very short, around a few seconds.

The ultrasonic vibration is concentrated in specific points present on the welding abutment.

The two lateral pressors secure the film in place during welding, eliminating any possibility of movement. The splice is linear.

The machinery of the patent reduces the possible error in film alignment during splicing because at present this operation is totally manual.